An engine system may be configured with a boosting device, such as a turbocharger, for providing a boosted air charge to increase torque output. In particular, a turbine is rotated using energy from an exhaust flow. The turbine drives a compressor which delivers a boosted air charge to the engine intake. An engine system may also be configured with an exhaust gas recirculation (EGR) system wherein at least a portion of the exhaust gas is recirculated to the engine intake. For example, the EGR system may be a low-pressure EGR system (LP-EGR) that recirculates exhaust gas from downstream of the turbine to upstream of the compressor. EGR benefits include an increase in engine dilution, decrease in exhaust emissions, and an increase in fuel economy.
An engine system may arbitrate multiple systems and actuators in order to increase fuel economy while providing acceptable vehicle performance. For example, reducing throttling losses is one example of an opportunity to increase fuel economy. However, throttling is also an approach for holding torque in reserve that is quickly and easily accessible to provide a quick pedal response (i.e., reduce response lag to produce torque output) to provide acceptable vehicle performance. Moreover, the LP-EGR system may complicate matters relating to response lag due to a large diluted volume of EGR in the LP-EGR system that may provide a torque shortfall.
To address these issues, engine control systems may employ various approaches for improving torque response to provide acceptable vehicle performance. In one example, a driver is required to increase a pedal angle (e.g., tip-in) to initiate a transient conditions mode that triggers pre-planned actions to increase torque output. Such pre-planned actions may include adjusting variable valve timing (VVT) maps to a maximum effective volume, a transmission event (e.g., a downshift), and increasing boost.
However, the inventors herein have identified issues with such approaches. For example, the driver may perceive a noticeable “dead/spongy pedal” zone with no driver observable torque increase before the pre-planned actions are triggered. Further, once the pre-planned actions are triggered, the resulting torque increase typically is greater than desired. For example, the excessive torque increase may require additional pedal correction by the driver (e.g., tip-out). Moreover, such pre-planned actions may forfeit fuel efficiency in favor of quickly increasing torque output.
In one example, the above issues may be at least partly addressed by a method for providing an appropriate torque response during transient conditions. In one embodiment, the method comprises during a transient condition, when a desired inlet manifold pressure is greater than a throttle inlet pressure of a first throttle, if a pressure drop across a second throttle that is positioned upstream from the first throttle in an intake passage is greater than a pressure threshold, opening the second throttle to increase the throttle inlet pressure.
For example, the first throttle may be an engine throttle and the second throttle may be an air intake system (AIS) throttle that draws EGR from a LP-EGR system into an intake passage. During such transient conditions, exhaust pressure may be high enough to provide a suitable mass flow of EGR that the AIS throttle may be redundant, and the AIS throttle may be opened to provide the increase in throttle inlet pressure without losing EGR control or forfeiting fuel economy. By opening the AIS throttle, air flow may be increased to provide just enough torque without substantially overshooting the torque demand.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.